Direct and Indirect Searches For Particle Dark Matter

1、The Observational Case For 7-8 GeV Dark Matter:Fermi, CoGeNT and DAMADan HooperFermilab/University of Chicago FermilabOctober 18, 2010Based onDark matter annihilation in the Galactic Center as seen by the Fermi Gamma Ray Space TelescopeDan Hooper and Lisa GoodenougharXivA consistent dark matter inte

2、rpretation for CoGeNT and DAMA/LIBRADan Hooper, Juan Collar, Jeter Hall, and Dan McKinsey PRD (in press), arXivEvidence For Dark MatterGalactic rotation curvesGravitational lensingLight element abundancesCosmic microwave background anisotropiesLarge scale structureDan Hooper - The Case For 7-8 GeV D

3、ark MatterEvidence For Dark MatterThere exists a wide variety of independent indications that dark matter existsEach of these observations infer dark matters presence through its gravitational influence Without observations of dark matters electroweak or other non-gravitational interactions, we are

4、unable to determine its particle natureDan Hooper - The Case For 7-8 GeV Dark MatterWIMP HuntingDirect DetectionIndirect Detection Collider SearchesThe Indirect Detection of Dark MatterDan Hooper - The Case For 7-8 GeV Dark MatterWIMP Annihilation Typical final states include heavy fermions, gauge o

5、r Higgs bosonsW+W-The Indirect Detection of Dark MatterDan Hooper - The Case For 7-8 GeV Dark MatterWIMP Annihilation Typical final states include heavy fermions, gauge or Higgs bosonsFragmentation/Decay Annihilation products decay and/or fragment into combinations of electrons, protons, deuterium,

6、neutrinos and gamma-raysW+W-e+qqp0The Indirect Detection of Dark MatterDan Hooper - The Case For 7-8 GeV Dark MatterWIMP Annihilation Typical final states include heavy fermions, gauge or Higgs bosonsFragmentation/Decay Annihilation products decay and/or fragment into combinations of electrons, prot

7、ons, deuterium, neutrinos and gamma-raysSynchrotron and Inverse Compton Relativistic electrons up-scatter starlight/CMB to MeV-GeV energies, and emit synchrotron photons via interactions with magnetic fieldsW+W-e+qqp0e+The Indirect Detection of Dark MatterDan Hooper - The Case For 7-8 GeV Dark Matte

8、rNeutrinos from annihilations in the core of the Sun Gamma Rays from annihilations in the galactic halo, near the galactic center, in dwarf galaxies, etc.Positrons/Antiprotons from annihilations throughout the galactic haloSynchrotron and Inverse Compton from electron/positron interactions with the

9、magnetic fields and radiation fields of the galaxy An Essential Test:Searches For Gamma Rays From Dark Matter Annihilations With Fermi Dan Hooper - The Case For 7-8 GeV Dark MatterThe Fermi Gamma Ray Space Telescope has been collecting data for more than two yearsIn August 2009, their first year dat

10、a became publicly availableFermis Large Area Telescope (LAT) possesses superior effective area (7000-8000 cm2), angular resolution (sub-degree), and energy resolution (10%) than its predecessor EGRET Unlike ground based gamma ray telescopes, Fermi observes the entire sky, and can study far lower ene

11、rgy emission (down to 300 MeV)Dan Hooper - The Case For 7-8 GeV Dark MatterDan Hooper - The Case For 7-8 GeV Dark MatterWhere To Look For Dark Matter With Fermi?Dan Hooper - The Case For 7-8 GeV Dark MatterWhere To Look For Dark Matter With Fermi?The Galactic Center-Brightest spot in the sky-Conside

12、rable astrophysical backgroundsDan Hooper - The Case For 7-8 GeV Dark MatterWhere To Look For Dark Matter With Fermi?The Galactic Center-Brightest spot in the sky-Considerable astrophysical backgroundsThe Galactic Halo-High statistics-Requires detailed model of galactic backgroundsDan Hooper - The C

13、ase For 7-8 GeV Dark MatterWhere To Look For Dark Matter With Fermi?The Galactic Center-Brightest spot in the sky-Considerable astrophysical backgroundsThe Galactic Halo-High statistics-Requires detailed model of galactic backgroundsIndividual Subhalos-Less signal-Low backgroundsDan Hooper - The Cas

14、e For 7-8 GeV Dark MatterWhere To Look For Dark Matter With Fermi?The Galactic Center-Brightest spot in the sky-Considerable astrophysical backgroundsThe Galactic Halo-High statistics-Requires detailed model of galactic backgroundsExtragalactic Background-High statistics -potentially difficult to id

15、entifyIndividual Subhalos-Less signal -Low backgroundsDan Hooper - The Case For 7-8 GeV Dark MatterDark Matter In The Galactic Center RegionDan Hooper - The Case For 7-8 GeV Dark MatterThe region surrounding the Galactic Center is complex; backgrounds present are not necessarily well understoodThis

16、does not, however, necessarily make searches for dark matter in this region intractableThe signal from dark matter annihilation is large in most benchmark models (typically hundreds of events per year)To separate dark matter annihilation products from backgrounds, we must focus on the distinct obser

17、vational features of these components Dark Matter In The Galactic Center RegionDan Hooper - The Case For 7-8 GeV Dark MatterThe characteristics of a signal from dark matter annihilations:1) Signal highly concentrated around the Galactic Center (but not entirely point-like)2) Distinctive “bump-like”

18、spectral featureAstrophysical Backgrounds In The Galactic Center RegionDan Hooper - The Case For 7-8 GeV Dark MatterKnown backgrounds of gamma rays from Inner Galaxy include:1) Pion decay gamma rays from cosmic ray proton interactions with gas (p+pp+p+0)2) Inverse Compton scattering of cosmic ray el

19、ectrons with radiation fields3) Bremsstrahlung4) Point sources (pulsars, supernova remnants, the supermassive black hole)Astrophysical Backgrounds In The Galactic Center RegionDan Hooper - The Case For 7-8 GeV Dark MatterMuch of the emission is concentrated along the disk, but a spherically symmetri

20、c component (associated with the Galactic Bulge) is also to be expectedThe Fermi First Source Catalog contains 69 point sources in the inner +/-15 of the Milky WayBuild a background model with a morphology of disk+bulge+known point sourcesAstrophysical Backgrounds In The Galactic Center RegionDan Ho

21、oper - The Case For 7-8 GeV Dark MatterFit one energy bin at a time, and one angular range around the Galactic Center (no assumptions about spectral shape, or radial dependance)Fit to intensity of the disk (allow to vary along the disk), width of the disk (gaussian), intensity of the flat (spherical

22、ly symmetric) componentInclude point sources, but do not float Provides a very good description of the overall features of the observed emission (between 2-10 from the Galactic Center) Dan Hooper - The Case For 7-8 GeV Dark MatterProvides a very good description of the overall features of the observ

23、ed emission (between 2-10 from the Galactic Center) Astrophysical Backgrounds In The Galactic Center RegionDan Hooper - The Case For 7-8 GeV Dark MatterBy combining the results from all energy bins, we can extract the spectrum of emission from the disk and bulge componentsSpectral shapes consistent

24、with gamma rays from pion decay and ICSDisk,Disk,Spherically Symmetric ComponentAstrophysical Backgrounds In The Galactic Center RegionDan Hooper - The Case For 7-8 GeV Dark MatterBy combining the results from all energy bins, we can extract the spectrum of emission from the disk and bulge component

25、sSpectral shapes consistent with gamma rays from pion decay and ICSSpectrum of disk emission does not discernibly vary along the disk; disk intensity fluctuates by 30%Spectral shape of the spherically symmetric component also does not vary, but intensity does (brighter closer to the Inner Galaxy)Wel

26、l described by a distribution of source emission that scales with rIn contrast, dark matter annihilation products are predicted to be more centrally concentrated r -2 for NFW (=1), or even steeper if adiabatic contraction is taken into accountThe Inner Two Degrees Around The Galactic CenterDan Hoope

27、r - The Case For 7-8 GeV Dark MatterIf the Fermi data contains a signal from dark matter annihilations in the Galactic Center, we should expect to see departures from the background model within the inner 1 degree The key will be to observe both the morphological and spectral transitions in the data

28、Dan Hooper - The Case For 7-8 GeV Dark MatterDashed=diskDotted=bulgeSolid=disk+bulgeOutside of 1 degrees from GC, background model does very wellDan Hooper - The Case For 7-8 GeV Dark MatterDashed=diskDotted=bulgeSolid=disk+bulgeOutside of 1 degrees from GC, background model does very well, backgrou

29、nds utterly fail to describe the dataA new component is clearly present in this inner region, with a spectrum peaking at 2-4 GeVDan Hooper - The Case For 7-8 GeV Dark MatterDashed=diskDotted=bulgeSolid=disk+bulgeBy studying the angular profile of the observed emission, we determine the intensity of

30、the new component to scale with r to r If interpreted as dark matter annihilations, this implies a dark matter distribution that scales as (r) r Dan Hooper - The Case For 7-8 GeV Dark MatterDashed=diskDotted=bulgeSolid=disk+bulgeBy studying the angular profile of the observed emission, we determine

31、the intensity of the new component to scale with r to r If interpreted as dark matter annihilations, this implies a dark matter distribution that scales as (r) r Emission From Our Galaxys Supermassive Black HoleDan Hooper - The Case For 7-8 GeV Dark MatterWe were able to separate the point-like emis

32、sion from the center of the Milky Way (presumably associated with the SMBH) Above 1 GeV, the observed spectrum agrees very well with an extrapolation of the power-law emission reported by HESS (above 200 GeV)The Spectrum Of The Excess EmissionDan Hooper - The Case For 7-8 GeV Dark MatterWe have been

33、 able to cleanly extract the spectrum of the excess emission (not disk, bulge, or known point sources)Sharply peaked emission around 1.5 to 4 GeVNo statistically significant excess above 6-7 GeV The Dark Matter InterpretationDan Hooper - The Case For 7-8 GeV Dark MatterThe spectral shape of the exce

34、ss can be well fit by a dark matter particle with a mass in the range of 7.3 to 9.2 GeV, annihilating primarily to +- (up to 20% to hadronic channels is OK)No other dark matter annihilation channels provide a good fitThe normalization of the signal requires the dark matter to have an annihilation cr

35、oss section of -27-26 cm3/sOther Interpretations?Dan Hooper - The Case For 7-8 GeV Dark MatterChallenges:Very concentrated emission (scales with r )Very strong spectral peakOther Interpretations?Dan Hooper - The Case For 7-8 GeV Dark MatterUnresolved Point Sources?Perhaps a population of 50 or more

36、unresolved points sources distributed throughout the inner tens of parsecs of the Milky Way could produce the observed signal - millisecond pulsars have been suggestedOther Interpretations?Dan Hooper - The Case For 7-8 GeV Dark MatterUnresolved Point Sources?Perhaps a population of 50 or more unreso

37、lved points sources distributed throughout the inner tens of parsecs of the Milky Way could produce the observed signal - millisecond pulsars have been suggestedTwo problems:1) Why so many in the inner 20 pc, and so few at 100 pc? -With typical pulsar kicks of 250-500 km/s, millisecond pulsars shoul

38、d escape the inner region of the galaxy, and be distributed no more steeply than r -2 (assuming that none are born outside of the inner tens of parcecs!) Other Interpretations?Dan Hooper - The Case For 7-8 GeV Dark MatterUnresolved Point Sources?Perhaps a population of 50 or more unresolved points s

39、ources distributed throughout the inner tens of parsecs of the Milky Way could produce the observed signal - millisecond pulsars have been suggestedTwo problems:1) Why so many in the inner 20 pc, and so few at 100 pc? -With typical pulsar kicks of 250-500 km/s, millisecond pulsars should escape the

40、inner region of the galaxy, and be distributed no more steeply than r -2 (assuming that none are born outside of the inner tens of parcecs!) 2) Of the 46 pulsars in FGSTs catalog, none has a spectrum as sharply peaked as is observed in the Inner GalaxyAverage observed pulsar spectrumOther Interpreta

41、tions?Dan Hooper - The Case For 7-8 GeV Dark MatterHardened Pion Decay Spectrum?Most of the GeV-scale gamma rays elsewhere come from cosmic ray proton interactions with gas, producing pions; perhaps this signal does too?Other Interpretations?Dan Hooper - The Case For 7-8 GeV Dark MatterHardened Pion

42、 Decay Spectrum?Most of the GeV-scale gamma rays elsewhere come from cosmic ray proton interactions with gas, producing pions; perhaps this signal does too?The spectral shape of pion decay gamma rays depends only on the spectral shape of the cosmic ray protonsTypical models (such as that contained i

43、n GALPROP) predict a shape like:Other Interpretations?Dan Hooper - The Case For 7-8 GeV Dark MatterHardened Pion Decay Spectrum?Most of the GeV-scale gamma rays elsewhere come from cosmic ray proton interactions with gas, producing pions; perhaps this signal does too?The spectral shape of pion decay

44、 gamma rays depends only on the spectral shape of the cosmic ray protonsTypical models (such as that contained in GALPROP) predict a shape like:Power-law proton spectra lead to:(unable to generate observed peak)Other Interpretations?Dan Hooper - The Case For 7-8 GeV Dark MatterHardened Pion Decay Sp

45、ectrum?Most of the GeV-scale gamma rays elsewhere come from cosmic ray proton interactions with gas, producing pions; perhaps this signal does too?The spectral shape of pion decay gamma rays depends only on the spectral shape of the cosmic ray protonsTypical models (such as that contained in GALPROP

46、) predict a shape like:Power-law proton spectra lead to:(unable to generate observed peak)To produce a 2-4 GeV peak, the proton spectrum must break strongly at 50 GeV (essentially requires a delta function at Ep=50 GeV)This solution appears highly implausibleOther Interpretations?Dan Hooper - The Ca

47、se For 7-8 GeV Dark MatterConfusion With The Galactic Center Point Source?Perhaps the point spread function of the FGST is worse than we think, which leads us to misinterpret the GC point source as extended emissionOther Interpretations?Dan Hooper - The Case For 7-8 GeV Dark MatterConfusion With The

48、 Galactic Center Point Source?Perhaps the point spread function of the FGST is worse than we think, which leads us to misinterpret the GC point source as extended emissionThis would require the PSF to be a factor of 3 wider than report by the FGST collaboration (which is entirely inconsistent with o

49、bserved widths of many other point sources)Any instrumental explanation would , but not the rest of the region we studied (or the rest of the sky) Other Interpretations?Dan Hooper - The Case For 7-8 GeV Dark MatterConfusion With The Galactic Center Point Source?Perhaps the point spread function of t

50、he FGST is worse than we think, which leads us to misinterpret the GC point source as extended emissionThis would require the PSF to be a factor of 3 wider than report by the FGST collaboration (which is entirely inconsistent with observed widths of many other point sources)Any instrumental explanat

51、ion would , but not the rest of the region we studied (or the rest of the sky) No known astrophysical sources or mechanisms, and no plausible instrumental effects can account for the observed excess Evidence From Direct DetectionDAMA/LIBRAOver the course of a year, the motion of the Earth around the

52、 Solar System is expected to induce a modulation in the dark matter scattering rateDan Hooper - The Case For 7-8 GeV Dark MatterDrukier, Freese, Spergel, PRD (1986)Evidence From Direct DetectionDAMA/LIBRAOver the course of a year, the motion of the Earth around the Solar System is expected to induce

53、 a modulation in the dark matter scattering rate The DAMA collaboration reports a modulation with a phase consistent with dark matter, )Dan Hooper - The Case For 7-8 GeV Dark MatterEvidence From Direct DetectionCoGeNTThe CoGeNT collaboration recently announced their observation of an excess of low e

54、nergy events Although it has less exposure than other direct detection experiments, CoGeNT is particularly well suited to look for low energy events (and low mass WIMPs)Dan Hooper - The Case For 7-8 GeV Dark MatterCoGeNT Collaboration, arXivCoGeNT and DAMAIntriguingly, if the CoGeNTand DAMA signals

55、are interpreted as the elastic scattering of dark matter, they point to a region of parameter space with mass of 6-8 GeV Recall that our analysis of the Galactic Center gamma rays requires dark matter with a mass of 7.3-9.2 GeVHooper, J. Collar, J. Hall, D. McKinsey, PRDFermi GC Mass RangeCoGeNT and

56、 DAMAAn example of a good fit:Hooper, J. Collar, J. Hall, D. McKinsey, PRDCoGeNT and DAMABut what about the null results of XENON and CDMS?Dont these rule out the DAMA/CoGeNT regions?A very heated discussion has surrounded this question in recent monthsXENON 100 Collaboration, March 2010CoGeNT and D

57、AMABut what about the null results of XENON and CDMS?Dont these rule out the DAMA/CoGeNT regions?This depends critically on the scintillation efficiency of liquid xenon - large uncertainties, no measurements below 4 keVThe XENON 100 collaboration initially used a set of (unreasonably) optimistic val

58、ues for LeffMore moderate values do not lead to a strong constraint on the CoGeNT/DAMA regionXENON 100 Collaboration, March 2010CoGeNT and DAMAMore stringent constraints come from XENON10 and CDMS (Si)Both appear in tension with most of the best fit CoGeNT/DAMA region, but at only 1Better determinat

59、ions of Leff and of the CDMS Si recoil energy calibration scale may clarify this situation in the future (both are in progress)See Savage, Freese, et al. (2010); J. Filippini thesis (2008)What Has Been Discovered Here? (comments on model building)Dan Hooper - The Case For 7-8 GeV Dark MatterRequirem

60、entsStable particle with a mass of 7-8 GeVAt non-relativistic velocities, annihilates primarily to +- (perhaps among other leptonic final states)Non-relativistic annihilation cross section (to +-27 cm3-26 cm3/s Elastic scattering cross section with nucleons of SI2x10-40 cm2 (from CoGeNT+DAMA)Are the